US2071643A - Distillation of oil - Google Patents

Description

F. L. MAKER Feb. 23, 1937,

DISTILLATION OF OIL Filed May 24, 1955 L1 -IL TUBULAR H67! 76/? m RES/000M DRAW OFF r 9 F6 Z m @M 0 UL z n 4 1% 1 tom fractionating plate.

Patented Feb. 23, 1937 UNiTED STATES PATENT GFFIQE DISTILLATEON OF OIL Application May 24, 1935, Serial No. 23,282

Claims.

This invention relates to the distillation of oil by a fractionation process and particularly to a method and means for adding heat to the liquid in the lower part of a fractionating column and 5 withdrawing stripped residuum therefrom.

In the practice of fractionating or stripping lighter components from a liquid mixture, it is usually necessary to add heat to the lower portion of a fractionating column, which heat is ll) carried upward through the column by means of vapors. This is commonly done by heating the reflux liquid in the bottom of the column, that has flowed from the fractionating plates above, and vaporizing a portion or all of it, which vapors,

together with any other fluid, such as steam, that may be added to promote distillation or reduce maximum temperatures or for other purposes, pass upward through the column acting as a vehicle for the heat. In continuous processes 20 a portion of the liquid in the lower part of the column is withdrawn continuously from a column as stripped product, or bottom, or residuum.

The reflux liquid overflowing from the bottom fractionating plate contains more light fractions 25 than is desired in the residuum or bottoms passing out of the column. It is therefore desirable to insure that all of the liquid coming from the bottom plates passes at least once over the heating surface before it has opportunity to pass out 30 through the bottom or residuum draw-off connection.

In some cases it has been the practice, in order to achieve this object, to pass over the heating surface only the liquid overflowing from the bot- This method has the objection that if there is any fluctuation of the rate of overflow from the bottom plate, there will be a change in the quantity of liquid passed over the heatingsurface, and if the heat input is con- 40 stant or nearly so, as is usual, there will be a corresponding inverse fluctuation of the temperature. The temperature of the liquid may rise to a higher point than is desirable or the heating surface may become overheated due to insufiicient liquid circulating over it to keep it cool. To

avoid this, it is desirable to circulate liquid over the heating surface at a greater rate than the rate of overflow from the bottom fractionating plate,

so that a portion of the circulating liquid is con- 50 tinuously recirculated.

With this arrangement, it is sometimes the practice to discharge the liquid overflowing from the bottom fractionating plate into the entrance pipe to the circulating and heating system, as in my copending application Serial No. 607,383 filed April 25, 1932, which matured into Patent No. 2,031,610 on February 25, 1936, so that the overflow or reflux liquid will be certain to pass at least once over the heating surface. This, however, has a disadvantage that the hotter liquid being 5 recirculated tends to cause vaporization in the heater system of the lighter components of the reflux liquid that has overflowed from the bottom fractionating plate, which liquid is always richer in the lower boiling components than is the residuum, and which is also at a lower temperature than the latter. This vaporization causes difliculty in pumping the liquid being circulated past the heating surface, and may become sufficiently aggravated, especially when the system is being operated at pressure less than atmospheric, to make the pump inoperative by so-called vapor-locking.

My invention comprehends a system of bafile means in the reservoir at the bottom of such a column and a mode of operation thereof that will insure proper and efficient operation, so that all entering reflux will be adequately heated, exposed to an extended surface to permit escape of light fractions and positively directed through the heating means.

It is an object of this invention to insure that all of the reflux liquid overflowing from the bottom fractionating plate passes over the heating surface at least once before it is withdrawn as residuum or bottoms.

It is also an object of this invention to provide a circulation rate over the heating surface that is greater than the rate of overflow of liquid from the bottom fractionating plate.

'A further object is to secure a mixing of the liquid overflowing from the bottom plate with the excess liquid that has just returned from being passed over the heating surface, whereby the lighter ends in the overflow liquid are evaporated '40 and removed from the liquid before it enters the circulating stream, so that vaporization does not take place in the circulating system.

Another object is to provide a definitely maintained direction of flow of reflux and residuum in the bottom of a fractionating column to insure adequate stripping thereof.

Another object is to provide a means and mode of operation that will reduce the vaporization and increase the capacity of a circulating pump and tubular heater in an installation of the character described.

Another object is to provide a method and means for operating a fractionating column that will prevent vapors from getting into and moving upwardly in a reflux conduit or downspout, thus insuring that the liquid downflow will not be interrupted or reversed and the column caused to head.

These and other objects and advantages will be more fully apparent from the following description and from the accompanying drawing, which forms a part of this specification, and illustrates a preferred embodiment of this invention.

The drawing is a diagrammatic and part sectional view of a fractionating column and a tubular heater therefor, the latter adapted to add heat to the reservoir at the bottom of the column, with a preferred arrangement of baffles in said reservoir to direct the flow therein.

Referring to the drawing, the numeral ID designates generally the fractionating column, which may be of the conventional type with a shell H, liquid-vapor contact plates l2, feed inlet i3, and vapor outlet 14. A reflux flow conduit 15 is provided from the bottom plate, said conduit extending downwardly into the reservoir IS in the bottom of the column.

An overflow weir or bailie l! is provided as a means for withdrawing circulating liquid from reservoir I6 and controls the flow of said liquid to the circulation outlet conduit is. Pump iii in conduit l8 urges the liquid through a conventional tubular heater 20 and back into reservoir it through conduit 2!.

Reservoir I6 is divided by a partition or partial bafile 22 intoa first chamber 23 and a second chamber 24, with a communicating passage 25 so that liquid may flow from the bottom of chamber 23 into chamber 24 for a purpose to be described below.

The heated liquid returns from heater 20 through conduit 2| to reservoir [6 over a spreader element 26 (optional) into said first chamber 23 and mixes with the residuum therein. Liquid from chamber 23 flows through passage 25 into second chamber 24, where it mixes with and imparts heat to the reflux liquid from conduit [5, which latter extends into said second chamber 24, as shown. The tar or residuum outlet conduit 21 from reservoir 16 extends into first chamber 23 and preferably to a point higher than the outlet of reflux conduit #5, so that a liquid seal will at all times be maintained for said latter conduit, thus preventing vapors in the reservoir l6 from entering the same, and interfering with the downward flow of liquid therethrough. The sealing relation just outlined for reflux conduit 45 is further maintained by the overflow weir i I which is preferably located at a point higher than the lower end of conduit l5, as will be apparent from the drawing. If such should occur, the fractionating column would tend to head and its operation would be upset.

In operation, the rate of circulation through conduit l8, pump l9, heater 2i! and conduit 2| is maintained at a rate higher than the rate of reflux flow from plates l2 through reflux conduit l5 into the second chamber 24 of reservoir l6. Thus the direction of flow of liquid in the Various chambers of reservoir 16 is always in the direction indicated by the arrows, or from first chamber 23 through passage 25 into second chamber This insures that no reflux from conduit IE will pass backwardly from chamber 25 into chamber 23 and go unstripped out of the tar or residuum draw 21.

As stated above the reflux from conduit i5 entering chamber 24 is at a lower temperature than the liquid in reservoir l6 generally, particularly that flowing from chamber 23 to chamber 24, and also contains lighter fractions. As the refluxenters chamber 24 it is mixed with the hotter liquid therein and, before passing into the circulating system it flows over weir i! thus being adequately exposed to the vapor space in the reservoir H3, so that the light fractions may be boiled off. The partially stripped reflux, mixed with the residuum liquid from chamber 23 then passes through the tubular heater 28, wherein more heat is added. Any vaporizable fractions remaining are released as the heated liquid from conduit 25 spreads over spreader member 26 or is exposed at the top of chamber 23. As also stated above, residuum may be continuously withdrawn through tar draw 27.

A further advantage of the initial and partial removal of the lighter fractions from the reflux by its contact in chamber 24 with hot recirculated residuum from chamber 23, and before it passes over weir I 1 into the circulating and heating system, is the decreased vaporization that takes place in the circulating pump l9 and tubular heater 2%, thus increasing the capacity and decreasing the carbon deposition in the latter.

It will readily be recognized that it is not necessary for the reservoir I6 and the fractionating column I!) to be in the same shell, as has been shown for convenience in this example, so long as reflux liquid can be passed from said column into said reservoir and vapor from said reservoir can be returned to said column.

Although a specific construction embodying this invention has been described and illustrated it is to be understood that the invention is not limited to that specific device or mode of operation described for it, and all such modifications and claims as come within the scope of the appended claims are embraced thereby.

I claim:

1. An apparatus for distilling oil comprising a fractionating column, a separate oil heater, a reservoir for liquid, means in said reservoir dividing the same into a first chamber and a second chamber, a substantially unrestricted passage for liquid from said first chamber to said second chamber, means for conducting reflux from said fractionating column into said second chamber, means for withdrawing liquid from said second chamber at a point higher than the outlet of said last named means, passing said liquid through said heater and returning said liquid to said first chamber, and means for passing vapors from both chambers of said reservoir directly into said fractionating column.

2. An apparatus according to claim 1 in which said reservoir is positioned in the lower part of said fractionating column and said reflux conducting means comprises a conduit for keeping said reflux out of contact with the vapors from said reservoir.

3. An apparatus for distilling oil, comprising a fractionating column, liquid-vapor contact plates in said column, a tubular oil heater, a reservoir in the bottom of said column, flow restricting means in said reservoir for dividing the same into a first chamber and a second chamber, conduit means for conducting reflux from the lowest plate in said column into said second chamber out of contact with the vapors from said reservoir, a circulating liquid conduit leading out of said second chamber to said heater from a point in said chamber higher than the outlet of said reflux conduit means to form a seal therefor, a pump in said last named conduit, a circulating fiuid conduit from said heater to said first chamber, and a residuum outlet from said first chamber.

4. An apparatus for distilling 011, comprising a fractionating column, liquid-vapor contact plates in said column, a tubular oil heater, a reservoir in the bottom of said column, a bafiie in said reservoir for dividing said reservoir into a first chamber and a second chamber, a liquid passage in the lower part of said baiiie, a conduit for refiux from the lowest plate in said column, said conduit terminating in the lower part of said second chamber and adapted to keep said reflux out of contact with the vapors from said reservoir, a level control weir in said second chamber, a conduit leading from behind said weir to said heater, a pump in said conduit, a return conduit from said heater to said first chamber, and a residuum outlet from said first chamber above the lower end of said reflux conduit, said outlet and said weir cooperating to form a liquid seal for said reflux conduit.

5. An apparatus for distilling 011 comprising a fractionating column, a reservoir divided into a first chamber and a second chamber, means for passing reflux from said column into said second chamber without contacting said reflux with vapors from said reservoir, means for withdrawing liquid from said second chamber at a point higher than the outlet of said last named means to form a seal for the same, means for heating said liquid, means for delivering it to said first chamber, and means for passing a portion of said heated liquid from said first chamber to said second chamber without substantial pressure drop.

FRANK L. MAKER.

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